1 Introduction
The fan gearbox is a transmission component that connects the fan shaft and the generator. It converts the low-speed input of the spindle into the output required by the medium-speed or high-speed generator and is one of the important components in the fan. Due to the complex working conditions of the fan gearbox and high requirements on reliability, the design and application of the fan gearbox, especially the selection, installation and use of the bearing as a key component are particularly important. Inappropriate bearing selection or improper installation and use can lead to various bearing damage and failure modes, and may even damage other components in the gearbox. These damages and failures will directly or indirectly cause the fan to stop. This will not only affect productivity, but also result in unplanned replacement and maintenance costs. Timken offers effective solutions for many common failure modes.
2. Common failure modes and solutions of fan gearbox bearings
Fan gearboxes are designed in a variety of ways, but they are basically made up of star and parallel grades. This paper takes the design of a planetary carrier as an input, a fixed ring gear, and a sun gear output and transmitted to a parallel stage as an example. The common failure modes of bearings and the corresponding solutions are analyzed and described.
2.1 Planetary carrier bearings
2.1.1 Common failure modes:
The selection and application of the planet carrier bearing is related to the design of the spindle. At present, the most common planet carrier bearing is a full-loaded cylindrical roller bearing. If the spindle bearings use spherical roller bearings, whether it is a 3-point support design for a single spherical roller bearing or a 4-point support design for two spherical roller bearings, due to the radial and axial self-aligning roller bearings. The presence of play, when the wind turbine is in the brake or other conditions in which the axial load alternates direction of rotation, the main shaft and the planet carrier connected behind it may move in the axial direction. At this time, if a cylindrical roller bearing is used as a carrier bearing, axial displacement from the main shaft will be transmitted to the cylindrical roller bearing of the planetary carrier because the inner and outer rings have a certain relative dislocation space in the axial direction. If the turbulent momentum is large enough, it will cause impact on the cylindrical roller bearing. Moreover, because the internal ring gear and the deceleration case body are integrated, the planetary roller and the planet carrier together with axial motion will also cause tooth surface wear on the planetary gears.
2.1.2 Solution:
Timken recommends the use of single-row tapered roller bearing straddle mounts to resolve the effects of axial turbulence on the planet wheels by preloading the tapered roller bearings. In addition, the load-bearing area of ​​the preloaded tapered roller bearing is optimized, the raceway stress is reduced, the rigidity of the planetary gear train is improved, and the external axial force transmitted from the outside into the gear carrier planet carrier end can be tolerated.
2.2 Planetary bearings
2.2.1 Common Failure Modes:
A common planetary roller bearing consists of a pair of double row cylindrical roller bearings. If the contact area between the outer ring of the bearing and the inner hole of the planetary wheel is insufficient or the contact area between the two is reduced due to the deformation of the gear, outer ring running and wearing may occur.
For the helical planetary gear design, due to the simultaneous axial force of the same size and opposite direction when the planetary gear meshes with the ring gear and the sun gear, the overturning moment generated causes the outer two rows of rollers to bear a large load. The middle two rows of rollers have a smaller load. The uneven load distribution between the four rows of rollers results in a certain difference in the actual service life. Under the premise of the same design life, the outer two columns will have premature flaking.
2.2.2 Solution:
The Timken integrated soft pin planet gear assembly is one of the best solutions to improve the star reliability of the line. The gear and bearing outer ring are integrated into one body to eliminate the possibility of running around the outer ring. At the same time, there are more internal space designs and larger rollers to improve the bearing capacity. By preloading two rows of tapered rollers, the load-bearing zone is optimized, reducing the risk of stress and roller slippage, and distributing the load more evenly across the two columns. The flexible pin design allows the planetary gear assembly to produce a flexible offset during operation, ensuring that the tooth surface has a high degree of engagement, especially for the design of a plurality of planetary gears, so that the load distribution between the planet gears becomes more uniform, and also Can reduce the processing and assembly accuracy requirements.
2.3 High-speed shaft bearings
2.3.1 Common failure modes:
Cylindrical roller bearings and four-point contact ball bearing combinations are common in high-speed applications. In the case of high speed and low load, cylindrical roller bearings are prone to roller slipping and raceway sliding, while ball bearings may suffer from scratches and micro spalling.
2.3.2 Solution:
Timken proposes cylindrical roller bearings with anti-wear coating and single row tapered roller bearings. Cylindrical roller bearings with a wear-resistant coating can continuously prevent slippage during the entire life cycle, and can also prevent raceway damage and poor lubrication due to impurities in the lubricant. Single-row tapered roller bearings can withstand radial and bidirectional axial loads, and their pure rolling characteristics minimize the possibility of scratches.
3. Summary
With the rapid development of the wind power equipment industry, especially the high-power fan is becoming more and more mainstream, the reliability of fans and parts will be the focus of research and development. The common failure modes and solutions for gearbox bearings introduced in this paper are designed to help equipment manufacturers select bearing solutions that are more suitable for fan gearbox applications, and strive to continuously optimize the design of the reducer so that the reliability of the gearbox and even the entire machine is A substantial increase.
Common bearing failure modes and solutions for fan gearboxes